Wave transmission



Marh 23, 1948. A. G. FOX

WAVE TRANSMISSION Filed Nov. 5, 1942 3 Sheets-Sheet 1 INVENTOR A. 6. FOX

March 23, 1948.

FIG. /0

A.- a. Fox 2,438,119-

WAVE TRANSMISS ION Filed Nov. 3, 1942 3 Sheets-Sheet s 4% L? W K ATTQRNEV Patented Mar. 23, 1948 UNITED. STATES ()FFICE A 2 .4mm

TRANsMissrcSn Arthur Gardner Fox, Morristown; N. J-.*,= assignor to Bell Telephone Laboratories, Incorporated; New York N. Y., a corporation of New York Application November 3, i942't-Serial- N6; 33?

(01. it's-44'') 46 Claims. 1

This invention relates to the transmission of guided electromagnetic waves and more particu larly' to phase changing devices for use in such transmission.

An object of the invention is to shift the phase ofa; guided electromagnetic wave through e ther a fixed or a variable angle, which may be either leading or lagging.

, Another object is to permit a wave guide to be rotated at a rotary joint either without changing the phase or without changing the polariza tion or the wave transmitted therethrough.

A further object is to separate guided waves in accordancewith their polarization.

It is known that a uniform metallic sheath with or without a dielectric filler may be used toguide suitable electromagnetic waves. In cross section the sheath may be circular, rectangular or of any other shape. For all frequencies above a minimum, known as the cut-off frequency, the guide behaves like a transmission line and has a specific propagation constant and characteristic impedance. For any particular frequency there are an-infinite number of cross;- sectional sizes and shapes ofguide which will have the same characteristic impedance;

It is often desired to shift the phase of a polarized electromagnetic wave through a fixed or a variable angle, as it passes a particular point in a: guide. In accordance with the invention there is provided an efficient phase shift sectionsuit able for this purpose comprising a section of wave guide having therein a plurality of polar shunt reactive elements spaced apart from each other." By a proper choice of the sign and=magnitude of the reactance, and the spacing interval, any desired phase shift, either leading Or lag ging, may be provided. For a leading phase" shift the reactances should be inductive and for a lagging phase shift they should-be capacitive at the frequency of interest. A suitable polar inductive element for a wave guide of-circular cross section is a diametral rod. The element may. be

made capacitive by providinga gap at the center of the rod. Two ormore reactances may; be used, depending upon the: over-all phase shift desired.

An application of the invention: is to a rotary joint. A 90-degree phase shift section on the input side produces a circular polarization of the wave as it passes through the joint. A second QO-degree section on the output side is oriented toproduce a linearly polarized wave parallel to the polarization of the terminating equipment. Rotation of the joint will; therefore, not change the alignment of the'wave'entering the receiver.

A variable phase changer may be provided by using two 90=degree phase shift sections with a rotatable ISO-degree phase shift section interposed; thereb'etwen'. This system may also be used asa' rotary joint to" transmit a linearly po lar-ized wave from a; fixedsource to" a rotating load without changeof hasewith rotations- To accomplish this, one QO-degree' phase shift section is associated with the source, theother 90 d-egres sectionis associated with the load and arranged torotate with it; and the 1'80 d-egree section isgeared to the load in suohaway that the" lso degree section rotates with angular velocity: which iS one=na1r that Of fihE' Made This last described system will also operate satisfac' torily if the" two 90=degreesectionsare omitted.

Another type of VariabIe phase Changer comprises a 90- d'egree section associatedwith a fi iied source, followed by a sc -degree rotatable sec tion and a ISO degree rotatable se'ction'. Now if the rotatable QO-degree" sect-ion is geared to the I=degree section so that the latter rotates through-- oiie half the angle or the former the system will deliverat its output a wave which may be changed in phasewithout a-= change-in polarization! Afi 'altefliative' system for ifitlodllci 'rlg an adjustable' phase shift without change polariza ti'dn comprises acmaegree section'associ-ateu with the fliied seu'r caa second degre'e section assoolatetl with the fixed load and two" I'SO degree se'ctic'ins interposed therebetw'eem The two degr'ee sections are so geared that they may be rotated: in opposite directions througli equal angles.

A sc -degree: phase shift section may be" used 5; semnrene-"ctmg system to convert a'iwave i-mear t elliptic-a1 or circular polarization. Fdr' ei'r aiiiple a wave guide may be fed at some pom by either a coaxial line" or a trier wave ii guide at 7 point offeed and he; hase shift s'ectioriis located either be tween the reflector aridth'e point of feed" or'ori the othefsideof thepointof fe'ed'. k

v Arhtatable Bouegreepmse shift sectionm'ay Befis'ea'm aware guide t'os'wi'tch linearly polariZedwaVes-as desired from oiie' toariotlier'df we branching wave guides havm suecnveaev ees therein If the ISO-degree section is replaced by a- QO -degree section the system will convert a wave from circular to linear polarization arid switch itto one or' the other of the branches, de-

pending upon the direction of rotation of the original wave.

The nature of the invention will be more fully understood from the fol-lowing detailed description and by reference to the accompanying drawings in which like reference characters refer to similar or corresponding parts and in which:

Fig. 1 is a perspective view, partly cut away, of a phase shift section using two inductive reactances to provide a, leading phase shift;

Fig. 2 is an end view of the phase shift section of Fig. 1, with the principal electrical axes indicated;

Fig. 3 shows a phase shift section similar to that of Fig. 1 but using three inductive reactances;

Fig. 4 is a perspective view, partly cut away, of

a phase shift section using two capacitive reactances to provide a lagging phase shift;

. Fig. 5 is a perspective view, partly cut away, of a rotary joint on either side of which is a phase shift section of the type shown in Fig. 1;

Fig. 6 is a perspective view, partly cut away, of a variable phase changer using two sections of the type shown in Fig. 1 and an interposed rotatable section of the type shown in Fig. 3;

Fig. '7 is a side view, partly in section, of a system for transmitting without phase shift a linearly polarized wave from a fixed source to a rotating load;

' Figs. 8 and 9 are side views, partly in section, of alternative systems for varying the phase shift without changing the polarization of a wave transmitted from a fixed source to a fixed load;

Figs. 10 and 11 are sectional views of alternative semireflecting systems using phase shift sections to convert a wave from linear to elliptical or circular polarization;

Fig. 12 is a cross-sectional view of a system using a rotatable 180-degree phase shift section to switch linearly polarized Waves from one to another of two branches; and

Fig. 13 is a cross-sectional view of a system using a rotatable 90-degree phase shift section to switch circularly polarized wavesfrom one or another of two branches.

Taking up the figures in more detail, Fig. 1 is a perspective view and Fig. 2 an end view of a phase shift section in accordance with the invention comprising a section of metallic Wave guide i of circular cross section having therein two polar shunt reactive elements 2 and 3 spaced apart a distance A. As shown, the elements 2 and 3 are of the inductive type and are constituted by two parallel metallic diametrai rods extending across the guide I. v I When a section of the type shown in Fig. 1 is properly adjusted, it has the property of retarding or advancing dominant transverse electric waves whose electric field is parallel to the elements 2 and 3, so that the phase of such waves after passing through the section will lag or lead the corresponding phase they would have had if the reactive elements 2 and 3 were not present. On the other hand, waves Whose electric field is perpendicular to the reactive elements will not be affected by their presence. If symmetric or non-polar shunt reactances, such as, for example, transverse partitions with circular apertures,

were used in place of the rods 2 and 3, the waves would undergo the same phase shift on passing through the section, regardless of their polarization. In contradistinction to this type, the phase shift sections referred to hereafter embody polar reactances, and the total phase shift of the transmitted waves will depend upon their initial polarization. In general, there will be one angle of polarization for which transmitted waves will suffer the greatest total amount of phase shift. There will be another polarization at right angles to the first for which waves will suffer the least total amount of phase shift on passing through the section. These two polarizations determine the principal electric axes of the section, indicated by the dot and dash lines M and N in Fig. 2. Such a section corresponds closely to the doubly refractive plates used in optics.

The number of electrical degrees net phase shift which is used hereinafter to designate these sections refers specifically to the difference between the total phase shifts suffered by waves of the two principal polarizations. In the case Where the shunt reactances have no effect on one polarization, the net phase shift will be the number of electrical degrees by which the reactances alter the total phase shift of waves of the quadrature polarization. Whether this net phase shift is leading or lagging depends fundamentally upon whether the reactances decrease or increase the effective length of the section. Capacitive shunt reactances increase the effective length while inductive shunt reactances decrease the effective length.

The magnitude of the desired phase shift determines the required reactances of the rods 2 and 3 which, in turn, are largely dependent upon the diameters of the rods. Once these diameters have been chosen, the spacing A between the rods 2 and 3 is determined by the wave-length to be transmitted. In practice it will usually be found that the final adjustment of the section is best made on an empirical basis. Two rods 2 and 3 of approximately the same diameter are assembled in the guide I and the spacing A is adjusted until resonance is obtained as indicated by maximum transmission and minimum reflection of power. The phase shift of the section is then measured. If this is too large the diameters of the rods 2 and 3 are reduced; if too small, the diameters are increased. The spacing A is again adjusted if required. These two steps are repeated, alternately, until the desired phase shift is obtained, with maximum transmission. As an example, the phase shift section of Figs. 1 and 2 may be designed and adjusted to provide a leading net phase shift of degrees in which case the spacing A will be approximately equal to A, where A is the wave-length within the guide at the frequency of interest.

' Theoretically a pair of shunt reactive elements are capable of producing any phase shift from zero to degrees, either leading or lagging. Practically, however, considerations of band width and transmission efficiency will limit the maximum useful phase shift to considerably less than 180 degrees. Where phase shifts of around 180 degrees or more are required, they may be obtained through the use of several sections of the type shown in Fig. 1, arranged in tandem, with all reactance elements parallel. If the spacing between sections is reduced to zero, it is evident that the end reactance elements of adjacent sections may be merged into common elements. Fig. 3 shows, for example, the combination of two such sections. The end diametral rods 5 and 1 will ordinarily have the same diameter, while the intermediate rod 6, which should have approximately only half th impedance of the end rods 5 and 1, will have a somewhat larger diameter. The distances B are-am V between the central rod Ban'd the end rods Stand 1', respectively, will ordinarily also be equal. This section may, for example, be designed to Have-a phase shiftof 180 degrees, in which case each'orithe spacing'sB and C'will be approximatei'yequalto An.

The section shown in Fig. 3 is fundamentally a band pass filter. VVhen" adjusted as described above, the peak of transmission and the desired phase shift will occur at only one frequency. However; by readjusting' the shunt reactances and their spacings, a band-pass characteristic may be obtained which will result in electrical characteristics forthe phase shift section which a're much less sensitive to frequency. It is, therefore, possible to attain a phase shift of any number of degrees in a section using a plurality of polar shunt reactances so adjusted as to produce a wide and substantially uniform transmission band, with low attenuation in the band.

For a lagging phase shift the reactances should he capacitive at the frequency of interest. Fig. dshows, for example, two capacitive elements 9 and l0- spaced apart a distance D in a circularguide I. The elements 9 and iii are parallel to each other and each is similar to the diametral rods-Z and- 3 of Fig. 1 but has a gap at its center as shown at H and I2. The capacitive reactance ofthe elements 9 and iii depends primarily upon the'diametral lengths of the gaps H and i2 and secondarily upon the diameters of the rods. Ordinarily the elements 9 and It are designed to haveapproximately equal capacitive reactance at the: frequency of interest.

Theifin-al adjustment is made by adjusting the length of the gaps II and I2 for the desired phase shift and the spacing D for maximum transmission in the manner explained above' in connection with Fig. 1. For the special case where a lagging phase shift of 90 degrees is desired, the distance D will be approximately For large phase shifts several sections of the type shown in Fig. 4- may be connected in tandem in th manner shown in Fig. 3.

It-should be pointed out that a lagging phase shiftmay be obtained by using several sections of-the'typeshown in Fig. 1 which add up to a total of more than 180 degrees leading. Also, a leading phase shift may be obtained by connesting; together a number of lagging sections suchas that of Fig. 4' to produce a lagging phase shift of more than 180 degrees.

90-degree phase shift section, either leading or lagging, may be used to convert an electromagnetic wave either from linear to circular or from circular to linear polarization. For example, if a linearly polarized wave is launched into a 90 degree phase shift section with the electric field at 45 degrees to the principal axes M and ofthesectlomit may be resolved into two components of equal amplitude polarized along the principal axes. These two components will be transmitted through the section without rotation, but there will be a relative phase shift of 90' degrees of one with respect to the other. Thus the emerging components will be oriented at right'angles to one another and they will also be" 90 degrees out of phase in time. The sum of these vectors must then result in a circularly polarized wave. Similarly any circularly polarized wave maybe resolved into two quadrature components which are linearly polarized parallel to the principal axes of a 90-degree phase shift sectionand are 90 degrees out of phase in time. After'passing through the section the addition of either plus or minus oil-degree phase shift to either of the components will make them in phase or degrees out of phase in time. In either case the sum of the two transmitted components will result in a linearly polarized wave at 45 degrees to the principal axes of the section.

The properties just described may be utilized in constructing a rotary joint in a wave guide, for use, for example, in a wave guide supplying energy to a rotating directive radiator. The problem is to keep the polarization of the'transmitted waves from rotating with respect to the terminating equipment as the joint is rotated, assuming that on either side of the joint the equipment rotates as a unit with the wave guide. Fig. 5 shows, for example, two sections of circular wave guide 14' and I5 terminating at their opposing ends in annular flanges l6 and l! to form a rotary joint. On" either side of the joint is a QO-degree phase shift section. These are of the inductive or leading type shown in Figs. 1

and 2. The one to the left comprises two parallel diametral rods l8 and I9 spaced apart a distance approximately equal to and the one to the right comprises two other parallel diametral rods 20 and 2| with like spacing. The distance between the end rods l9 and 20 should be at least of the order of M4. It is to be understood that capacitive or lagging type Elli-degree phase shift sections, such as shown in Fig. 4, may be substituted for those shown in Fig. 5. The two rods on the input side, for example it and iii, are oriented at 45 degrees to the incoming linearly polarized wave. The wave is converted by the first phase shift section into a circularly polarized wave which passes through the rotary joint. The two rods 20 and 2| on the output side are oriented so as to produce a linearly polarized output parallel to the direction of polarization of the terminating equipment, not shown. Rotation of the rotary joint will not change the alignment of the wave entering the receiving equipment. However, the device has an over-all phase shift which varies with th relative orientation of the two sections I l and I5 and it may, therefore, be used as a variable phase changer.

The flanges it and H in Fig. 5, and similar flanges shown in subsequent figures, are used at a gap in a wave guide primarily to reduce the reflection which would otherwise occur. The radial extent K of the flange is preferably adjusted for minimum reflection of the waves transmitted through the guide. In practical cases the optimum value of K will be in the neighborhood of M4, or somewhat less.

A 180-degree phase shift section has the property that linearly polarized waves upon being transmitted through the section will emerge linearly polarized, but their polarization will have been rotated by an amount dependent upon the relative angle between the incident polarization and the principal axes- M and N of the section. If circularly polarized waves are transmitted through the section, they will emerge circularly polarized, but the instantaneous polarization of the electric field will have been rotated with respect to the instantaneous polarization of the input by an amount depending upon the relative angle between the instantaneous input polarization and the principal axes of the section.

This latter property is made use of in the variable phase changer shown in Fig. 6 which comprises a rotatable 180-degree section inserted between two 90-degree sections. The IBO-degree section is similar to the one of Fig. 3, comprising a circular section of guide 23 with annular flanges '24, 25 at its ends and three spaced, parallel, diametral rods 5, 6 and 1. The two 90- degree sections l4 and I5 are of the type shown and described in connection with Fig. 5. It is assumed here, however, that the sections l4 and I5 do not rotate. The parallel diametral rods i8 and I9 in the section M are oriented at 45 degrees to the linearly polarized wave approaching from the left, and this section converts the wave to a circularly polarized one. The section 23 reverses the direction of rotation and alters the instantaneous orientation of the emerging wave in accordance with the orientation of the section. The section |5 reconverts the wave from circular to linear polarization. The parallel diametral rods 23 and 2| in the section l5 are oriented at 45 degrees to the direction of polarization of the terminating equipment, not shown, to produce a linearly polarized output parallel thereto.

As is seen above, the rotation of the central section 23 about its axis produces no change in the polarization of the output wave. It does, however, produce a time phase change in the oscillation which is substantially directly proportional to the angle through which section 23 is rotated. Furthermore, for a given direction of rotation, the sense of the time phase shift may be either positive or negative, depending upon which is used of the two possible 45-degree orientations of the electric vector of the incident wave with respect to the rods 5 8 and iii in the first section |4.

As mentioned above, the rotary joint shown in Fig. 5 introduces a phase shift. Fig. 7 shows a rotary joint in which this phase shift may be eliminated. The system comprises two 90-degree sections i4 and I5 and an interposed 180- degree section 28 similar to the corresponding sections of Fig. 6. The receiver is associated with the section i5 which, in this case, is arranged to rotate in the bearing 21 formed in the support 28. The central section 23 rotates in the bearing 30 formed in the support 3i and the section I4 is fixedly supported by the member 32. to the base 33 by means of brackets such as 34. In order to eliminate the phase shift the section i5 is geared to the section 23 so that the latter rotates through one-half of the angular displacement of the former. This is done by means of the two gears 36 and 31 fixed, respectively, to the sections 23 and i5 and the two gears 38 and 39 fixed to the shaft 40 which rotates in the bearings 4| and 42 in the supports 26 and 3|. The crank 43 is provided to turn the shaft 40. A linearly polarized wave entering the system at the left will .be converted to a circularly polarized wave by the section M, in which form it will pass through 'both rotary joints 45 and 45, and then be reconverted to a linearly polarized wave by the section IS, without any over-all phase shift in the system.

In Fig. 7 if the two 90-degree sections it and i5 are omitted the system may still be used to project linearly polarized waves from a fixed source into a rotating guide while maintaining the polarization of dominant Waves fixed with respect to the rotating section. This modified system will also serve to transfer circularly polarized waves across a rotary joint without change in phase with orientation of the rotating section.

The supports 28, 3| and 32 are fastened Fig, 8 shows another system for introducing a controllable amount of phase shift without changing the direction of polarization. The system includes a fixed 90-degree section l4, associated with the source, a rotatable 180-degree section 23, both similar to the corresponding sections of Fig. 7, and interposed therebetween a rotatable QO-degree section 50 with diametral rods 5|, 52 and end flanges 53, 54. The sections 53 and 23 are supported, respectively, by the supports 28 and 3| and are connected by the gears 31, 39, 38 and 36 and the shaft 40. The diameters of the gears are so proportioned that, when the shaft 43 is turned by means of the crank 43, the section 23 rotates through one-half the angle through which the section 50 rotates. The emerging wave is conducted to the receiver through a fixed section of guide 56 with an annular flange 51 at its end, supported by the member 58. If the input wave entering section I4 is polarized in a direction making an angle of 45 degrees with the parallel rods 8 and I9 and if all of the other rods 5|, 52, 5, 6 and 1 are lined up parallel to the rods 8 and IS the system will introduce neither phase shift nor rotation of polarization. However, if the section 50 is rotated through an angle, and the section 23 is rotated through half the angle, by means of the crank 43 and the gear train, a corresponding phase shift will be introduced as the wave passes through the system but there will be no rotation of polarization.

Fig. 9 shows an alternative system to that of Fig. 8 for introducing an adjustable amount of phase shift without rotation of polarization. The system includes a fixed QO-degree section l4 and a rotatable ISO-degree section 23 similar to the corresponding sections of Fig. 8. The section 50, however, is replaced by a second rotatable 180- degree section 63 having end flanges BI, 62 and parallel diametral rods 63, 64 and 65, supported by the member 66. The system is terminated in a fixed 90-degree section 61 having an end flange 38 and diametral rods 69 and 10 which are parallel to the rods l3 and IS. The receiver is associated with the output section 61 and so oriented that its direction of polarization makes an angle of 45 degrees with the axes of the rods 69 and iii. The sections 23 and 6|] are connected through the train of bevel gears l2, l3 and 14. The gears 12 and 74 are of the same diameter and are fastened, respectively, to the sections 23 and 60. The intermediate gear 13 has associated therewith a crank 15 which turns in the bearing 16 in the member 11 extending between the supports 3| and 66. Turning the crank 14 causes the sections 23 and 60 to rotate through equal angles but in opposite directions. The amount of phase shift introduced depends upon the orientation of the rods 63, 64 and with respect to the rods l8 and I9, but there is no over-all rotation of the polarization of the wave as it passes through the system.

It should be pointed out that a 90-degree section such as is shown in Fig. 1 or Fig. 4 may be inserted in a wave guide carrying an elliptically polarized wave to convert it to a linearly polarized wave. In this case the diametral rods are oriented parallel to either the major or the minor axis of the ellipse,

Another use for a 90degree section is to convert from linear to circular or elliptical polarization. Fig. 10 shows a system comprising a rotatable QO-degree section 50 interposed between two fixed sections of circular guide 80 and 8|. Electromagnetic waves polarized in a fixed direction aretedinto the system from a coaxial line 82 comprisinga cylindrical outer conductor 83, conto the section 80-, and a concentric inner conductor 84- which extends across the section 89 to form a diametral rodtherein. Impedance transformation for the coaxial line 82 is provided, when required, by the stub line 85 within which the inner conductor 84-is terminated by the slid, able reflecting piston 85. The position of the piston 861s. adjustedfor a match of the resistance components of the characteristic impedances of the line 82 and the section of guide 893. Any reactive: component associated with the inner conductor 84 may. in eflect,be annulled by ad-.

justing the position oi. the slidable reflecting piston 81 which closes the section St at the left. The pistons 8t and 81 are adjusted, alternately. until the maximum transmission of energy across the junction is attained. For this condition the spacing between the conductor 84 and the piston 81 will. generally be. approximately M4. By adjusting. the orientation. of the rotatable section 50 the system may be made to project into the fixed section. 8.!v waves having any desired degree of elliptical polarization. As a specialcase, circular polarization will be produced when the plane defined by the axes of the rods El and 52 makes. an. angle of 45 degrees with the direction 01 the-linearly polarized waves impressed upon the section 50. In order to simplify the draw ings, in. Fig.. 10, and also in Figs. 11 and 12, the supports arenot shown but these may, for example, be of the type shown in Figs. 7, 8 and 9.

Fig. 11-. shows an alternative arrangement of the. system. of. Fig. 10,. in. which the coaxial line 82 ieeds into. the section 8| instead of the section 80. In. this case the impedance presented by the coaxial line. 82 should be only half the characteristlc impedanceoi the wave guide section 8 l. The elli'pticity of polarization of the resultant wave may be controlled by movement of the piston 8'! provided the 90-degree section 59 is oriented with its principal axes at 4'5 degrees to the inner conductor 8'4. In either of the systems shown in Figs. 10 and 11. a wave guide may, of course, be substituted for the coaxial line 83 to feed the system.

Elg. 121's a cross-sectional view of. a system for switchingv a. guided linearly polarized wave from one branch to another. The system comprises a main. section or wave guide 89, a ISO-degree rotor section 23., two branches. 901 and 9| and selective devices associated with the branches all and ill. All oi the. sections are of circular cross section, sections 23 and. 89' are in. axial alignment and each of the sections 90 and 91 makes an angle F with the. section. 23,.

When the angle F is 120 degrees the selective.

devices may be diametral rods such as 32 and 93. spaced from the junction 94' the distances G and H, respectively, and preferably terminating in short. coaxial stubs 9 5 and S6 of length J. The rod; 92. lies in the plane of the junction, determined by the longitudinal mechanical axes of the branches 9!} and. BI, and the rod 93 is perpendicular to. this. plane. If a linearly polarized wave is sent into-the: section 89, rotation of the. section 23 will cause the direction of polarization of the transmitted wave to rotate so that at one time it is: parallel. to the rod 93 and at another time it has a component which is parallel to the rod 92.

- By properly adjusting the length J of the stubs 95 and 95 the rods 92' and .93 may be made to reflect waves polarized parallel to themselves, while freely passing waves polarized perpendicular thereto. Furthermore, distances G and H are rods 92 and 93 will be freely transmitted into the other branch. It follows, then, that for one orientation of the section 23, all of the power will be delivered to the branch 9%.]. As this orientation is changed through degrees all of the power is gradually diverted into the branch 9 I. There are, therefore, two switching cycles for one revolution oithe rotor section 23 and the voltage of the waves entering each branch is a sinusoidal function of the orientation of the rotor 23. When the system has been properly designed the attenuation introduced as the wave is switched from; one branch to the other is negligible.

The system shown in Fig. 12 may be used as a selector or a mixer for two linearly polarized waves polarized at 90 degrees with respect to one another and introduced into the section 89. For one orientation of the rotor 23, one of the waves will be entirely divertedinto the branch 98 and the other, into the branch 9!. Other orientations of the rotor 23 will permit part of each wave to enter each of the branches and thus the waves may be'mixed in any proportions desired.

If the angle F has a value other than degrees corrective shunt impedances, shown dia grammatically in Fig. 12 as X1 and X2, must be provided in the branches 9i] and!!! beyond the' rods 82 and 33. These impedances are primarily reactances and may be either polar or non-polar. A suitable non-polar impedance is a transverse partition with a central circular aperture. A suitable polar impedance is a diametral rod either with or without a central gap therein. If rods are used, the one in the branch 90 should be perpendicular to the plane of the junction and the one in the branch 9| should lie in that plane. The magnitude and sign of the impedances X1 and X2, and their distances from the junction M, are dependent upon the choice of the angle F. Each impedance is placed at a distance beyond the rod 92 or 93 determined by trial to be the one resulting in minimum reflection at the junction. This condition is evidenced by the inability to detect a standing wave in the main lloranch 89 when waves are introduced from the eft.

Fig. 13 is a cross-sectional view 'of a system for switching a circularly polarized wave into one or the other of two branches, depending upon the direction of rotation of the wave. The system is similar to that of Fig. 12 except that the degree rotatable section 23 has been replaced by, a rotatable QO-degree section 50. If the section 58 is so oriented that the rods 5i and 52 make an angle of i5 degrees with the plane of the junctioma circularly polarized wave entering the section 89 at the left will, as it passes the rods 5| and 52, be converted into a linearly polarized wave parallel to one of the rods 92 and 93, say92, which will act as a reflector therefor. However, since the rod 93 is perpendicular to the plane of the junction it will permit free passage of the wave along the branch 9!. On the otherhand, if the wave entering the section 89 had been ro-, tating in the other direction it is apparent that. it would be blocked from the branch 9| by the rod 83 but would be freely transmitted through the branch 95], past the rod 92. By rotating the section 5!) to other angles the incoming wave may be divided as desired between the two branches all and M.

The system shown in Fig. 13 may be used as a selector or a mixer for two circularly polarized;

waves, rotating in opposite directions, fed into the section 89. When the rods and 52 are oriented at 45 degrees to the plane of the junction one of the waves will be shunted into the branch 90 and the other into the branch 9|. By employing other appropriate angles any desired proportions of the two waves may be diverted into either of the branches.

What is claimed is:

1. A phase shift section for guided electromagnetic waves comprising a wave guide and three spaced polar reactive impedances connected in shunt thereto, the reactances of said impedances being chosen to provide the desired phase shift at a certain frequency, the spacing between said impedances being adjusted for maximum transmission of energy at said frequency, and the intermediate of said impedances having a reactance ap roximately half as large as the reactance of each of the other of said impedances.

2. A phase shift section in accordance with claim 1 in which said impedances are inductive.

3. A phase shift section in accordance with 7 claim 1 in which the desired phase shift is 180 degrees.

4. A phase shift section in accordance with claim 1 in which the spacing between successive impedances is approximately three-eighths of a wave-length.

5. A phase shift section in accordance with claim 1 in which said impedances are transverse rods within said guide.

6. A phase shift section in accordance with claim 1 in which said guide is, of circular cross section and said impedances are diametral rods.

'7. In a wave guide, a rotary joint for transmitting a linearly polarized electromagnetic wave from a source to a rotating load comprising means on the input side for converting from linear to circular polarization, means on the output side for reconverting to linear polarization, and an interposed rotatable 180-degree phase shift section.

8. A rotary joint in accordance with claim 7 in which said means comprise a 90-degree phase shift section.

9. A rotary joint in accordance with claim 7 in which said means comprise a section of cylindrical wave guide and a pluralitycf diametral rods therein.

10. A rotary joint in accordance with claim 7 in which said means comprise a sectionof cylindrical wave guide and two parallel diametral rods therein, said rods being spaced apart approximately three-eighths of a wave-length at the frequency of interest.

11. In a wave guide, the combination of two 90-degree phase shift sections and a rotatable 180-degree phase shift section interposed therebetween.

12. The combination in accordance with claim 11 in which each of said phase shift sections comprises a section of cylindrical wave guide and a plurality of parallel diametral rods therein.

13. The combination in accordance with claim 11 in which said 180-degree phase shift section comprises a section of cylindrical wave guide having an annular flange at each end thereof.

14. The combination in accordance with claim 11 in which said 180-degree phase shift section comprises a section of cylindrical wave guide and three parallel diametral rods therein, said rods being spaced apart approximately threeeighths of a wave-length.

15. In a wave guide a rotary joint for transmitting without phase shift a linearly polarized electromagnetic wave from a source to a rotating load comprising a fixed section of wave guide, a rotatable section of wave guide and a rotatable 180-degree phase shift section interposed therebetween, said phase shift section being geared to said rotatable section of guide in such a way as to rotate through one-half of the angular displacement of said rotatable section of guide.

16. A rotary joint in accordance with claim 15 which includes two -degree phase shift sections associated, respectively, with said fixed section and said rotatable section of guide.

17. A rotary joint in accordance with claim 15 in which said phase shift section comprises a section of cylindrical wave guide and three diametral rods therein.

18. A system for converting a guided electromagnetic wave from linear to elliptical polarization comprising a wave guide, a reflector in said guide, a rotatable QO-degree phase shift section associated with said guide and means for feeding energy into said guide, said phase shift section being located between said reflector and the point at which energy is fed into said guide and comprising aplurality of polar shunt reactive elements.

19. A system in accordance with claim 18 in which said phase shift section comprises a cylindrical section of wave guide and a pluralit of diametral rods therein.

20. A system in accordance with claim 18 in which the location of said reflector in said wave guide is adjustable.

21. A system in accordance with claim 18 in which said energy feeding means comprise a coaxial line including an inner conductor which extends diametrically across said Wave guide, the principal axes of said phase shift section being oriented at an angle of approximately 45 degrees to said inner conductor.

22. A system for switching a guided electromagnetic wave into one or the other of two branches comprising a main section of wave guide. two branches making equal angles therewith, selective devices in said branches responsive to different directions of polarization and a rotatable phase shift section associated with said main section, said phase shift section comprising a plurality of polar shunt reactive elements,

23. A system in accordance with claim 22 in which said phase shift section has a net phase shift of 180 degrees.

24. A system in accordance with claim 22 in which each of said equal angles is approximately degrees.

25. A system in accordance with claim 22 in which said branches have longitudinal mechanical axes lying in the same plane, the selective device in one of said branches comprises a transverse rod parallel to said plane and the selective device in the other of said branches comprises a. second transverse rod perpendicular to said plane.

26. A system in accordance with claim 22 in which one of said selective devices comprises a' impedance, said reflector being located at a distance from the junction of said branches so chosen that waves reflected by said reflector will be freely transmitted into the other of said branches and said corrective impedance being located ata distance from said reflector chosen to provide minimum reflection at said junction.

30. A system for switching a linearly polarized guided electromagnetic wave from one branch to another comprising a main section of wave guide, two branches making equal angles therewith, selective devices in said branches responsive to different directions of polarization and a rotatable ISO-degree phase shift section associated with said main section, said phase shift section comprising a plurality of polar shunt reactive elements.

31. A system in accordance with claim 30 in which said main section and said branches have longitudinal mechanical axes lying in the same plane and the principalelectrical axes of said phase shift section are so oriented with respect to said plane that said wave is diverted into one only of said branches.

32. A system in accordance with claim 30 in which each of said equal angles is approximately 120 degrees. I

33. A system in accordance with claim 30 in which said branches have longitudinal mechanical axes lying in the same plane, the selective device in one of said branches comprises a transverse rod parallel to said plane and the selective device in the other of said branches comprises a second transverse rod perpendicular to said plane.

34. A system in accordance with claim 30 in which each of said selective devices comprises a transverse rod terminating at each end in a coaxial stub.

35. A system in accordance with claim 30 in which said selective devices are polar reflectors located at distances from the junction of said branches so chosen that waves reflected by each of said devices will be freely transmitted into the other of said branches.

36. The combination in accordance with claim 11 in which each of said QO-degree phase shift sections comprises a section of cylindrical wave guide and two parallel diametral rods therein, said rods being spaced apart approximately three-eighths of a wave-length.

37. The combination in accordance with claim 11 in which each of said phase shift sections comprises a section of cylindrical wave guide and a plurality of parallel diametral rods therein, said rods being spaced apart approximately three-eighths of a wave-length.

38. The combination in accordance with claim 11 in which each of said sections comprises a plurality of spaced polar reactive impedances.

39. The combination in accordance with claim 11 in which each of said sections comprises a plurality of polar reactive impedances, said impedances being spaced apart approximately three-eighths of a wave-length.

40. The combination in accordance with claim 11 in which one of said QO-degree phase shift sections is rotatable.

41. In combination, two sections of wave guide, one of which is fixed, and an interposed phase shift section, said phase shift section comprising a plurality of spaced polar reactive impedances, having a phase shift of degrees and being rotatable about its longitudinal axis.

42. The combination in accordance with claim 41 in which said impedances are diametral rods.

43. The combination in accordance with claim 41 in which said impedances are diametral rods, said rods being spaced apart approximately three-eighths of a wave-length.

44. In combination, two sections of wave guide, one of which is fixed, and an interposed phase shift section, said phase shift section comprising a plurality of spaced polar reactive impedances and being rotatable about its longitudinal axis, each end of said phase. shift section and the ends of said other sections adjacent thereto having annular flanges extending outwardly for a distance approximately equal to a quarter of a wave-length.

45. In combination, two sections of wave guide, one of which is fixed, and an interposed phase shift section, said phase shift section being rotatable about its longitudinal axis and comprising three spaced polar reactive impedances, the intermediate impedance having a reactance approximately half as large as the reactance of each of the other impedances.

46. In combination, two sections of wave guide, one of which is fixed, and an interposed phase shift section, said phase shift section being r0- tatable about its longitudinal axis and comprising three spaced polar reactive impedances in the form of diametral rods, the intermediate rod having a reactance approximately half as large as the reactance of each of the other rods.

ARTHUR GARDNER FOX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,712 Southworth Sept. 13, 1938 2,155,508 Schelkunoif Apr. 25, 1939 2,257,783 Bowen Oct. '7, 1941 2,232,179 King Feb. 18, 1941 

